Functions of an EVA Encapsulant - Adhesion
Encapsulants are polymer-based sheets used to laminate PV cells. Two layers of Encapsulants are used in every module, with the Solar PV Cells sandwiched in between.
The key function of an Encapsulant is to protect the PV Cells from mechanical shock, act as a barrier from dust and moisture, provide electrical insulation, and prevent PID. The encapsulants form a layer around the cells, allowing the sunlight to pass through while blocking the harmful spectrum of UV radiation.
Why is adhesion Important?
Good adhesion / Peel Bond results in secured encapsulation, which in turn results in the integrity of the module. This means that the module will not fall apart even in harsh weather conditions like rain and extreme heat or cold and that the modules will continue to generate optimal power. Thus, this directly impacts the longevity of the module and the system.
Module defects/failures related to improper adhesion:
PV Modules are designed to operate for 25 years in terrestrial environments. However, mechanical stress, moisture, and ultraviolet radiation do cause some degradation in the protective materials in modules, including their adhesion properties.
These can potentially lead to solar cells being damaged by the external environment and compromise their performance.
Despite the importance of interfacial adhesion to module reliability, currently, there are no accurate techniques for characterizing module adhesion properties.
The specific module failures related to improper adhesion are:
A decrease in light passes through the layers of the module, resulting in lower power generation, as the light scatters away from the cell.
How peel bond test is performed?
A rectangular specimen is cut from the film. The layers are separated at the interface the adhesion is to be measured. The separated ends are known as the peel arms. These peel arms are clamped in the jaws of a tensile tester and pulled apart at a constant speed. The force to pull the peel arms apart is recorded. Peel strength is reported as the peel force divided by the specimen width. The angle, peel speed, specimen width, and temperature all influence the peel strength result.
The Peel Test is performed to:
Assess the uniformity of the adhesion
Distinguish between acceptable and unacceptable Encapsulant compositions, and module lamination recipes, by determining the adhesive strength range which is needed for a module to successfully generate power through its 25-year lifespan